Validity of a non-linear heart rate variability index for intensity threshold determination in chronic heart failure patients

Experiencing an increasing incidence, chronic heart failure (CHF) demands effective prevention and treatment. Aerobic exercise-based cardiac rehabilitation plays a vital role in managing these patients. However, diverse patient responses underscore the need for precision in intensity prescription. Heart rate variability (HRV), specifically the DFA a1 index, emerges as a cost-effective biomarker for exercise intensity distribution (Rogers et al., 2021a). Previous associations between HRV and ventilatory thresholds in CHF patients suggest its potential utility (Rogers et al., 2021b). This study aims to evaluate the agreement between ventilatory thresholds (VT1 and VT2) and HRV thresholds (HRVT1 and HRVT2) in male and female CHF patients during a cardiopulmonary exercise test. Seventeen males and ten females performed a symptom-limited incremental ramp test on a cycle ergometer. Ventilatory thresholds were determined using a mixed method, and HRV thresholds were calculated using DFA a1 values of 0.75 and 0.5 as the first and second thresholds, respectively. Statistical measures, including the Pearson’s r correlation coefficient, determination coefficient, and Bland-Altman plot with limits of agreement (LoAs), were employed to evaluate the agreement between these methods. Initial findings indicate that HRVT1 shows a non-significant, low positive correlation (r = .36) with VT1, with a determination coefficient of .13, and a mean bias of -5 bpm (LoAs from -35 to 25 bpm). Conversely, HRVT2 demonstrates a significant, strong positive correlation with VT2 (r = .78), presenting a determination coefficient of .62 and a mean bias of 6 bpm (LoAs from -16 to 28 bpm). This suggests promising potential validity for HRVT2 in estimating ventilatory thresholds. In conclusion, while HRVT1 requires further investigation in this population and caution is advised in its application, HRVT2 emerges as a compelling candidate, demonstrating good agreement with VT2 and suggesting its potential validity as a valuable tool for exercise intensity determination in CHF patients.